?Pilot study of African-specific variants and chronic kidney disease The over-arching goal of this pilot study is to provide additional data to support a larger R01 application that defines new directions for the roles of African-specific risk alleles (APOL1 and the sickle cell trait [SCT] rs334 variant), and novel genetic and environmental modifiers of APOL1 and SCT, on risk of chronic kidney disease and end-stage renal disease in African Americans. Our main goal is to better understand the clinically observed varying kidney disease risk and progression in African Americans carrying these high risk genotypes. Chronic kidney disease is a devastating condition associated with substantial cardiovascular disease burden, and socio-economic cost. APOL1 risk alleles confer 5- to 29-fold increased risk to end-stage renal disease in case-control studies, but only a 2-fold risk to chronic kidney disease in population studies. The role of SCT in progression to end-stage renal disease remains unclear. Our research hypothesis is that as yet unidentified genetic and environmental factors explain the variable clinical penetrance of chronic kidney disease in individuals with these risk alleles. Leveraging the existing, but untapped biorepository resource of the largest population-based longitudinal data set of African Americans in the U.S., we will perform baseline serum creatinine measurements in 3,826 African American women from the Women?s Health Initiative, to allow an unprecedented examination of the risk and progression of chronic kidney disease associated with APOL1 and SCT in African Americans.